The field of the disclosure relates generally to blower assemblies, and more specifically, to blower assemblies that include an impeller for attenuating blade pass tones.
Blowers and impellers are commonly used for creating a flow of either a gas or a liquid. More specifically, blowers and impellers may be used in the automotive and air handling and ventilation industries for directing large volumes of forced air, over a wide range of pressures, through a variety of air conditioning components. At least some known impellers use one or a combination of four basic blade designs: radial, forward curved, backward inclined, and backward curved. At least some forward curved impellers include a large number of blades that generally curve in the direction of a wheel hub's rotation, and backward curved impellers have blades that curve against the direction of the wheel hub's rotation. Generally, radial bladed impellers may have fewer blades than forward curved and backward curved designs, and are less efficient than forward curved, backward inclined, and backward curved designs. In addition, backward curved impellers are generally more efficient than forward curved impellers, backward inclined impellers, and radial bladed impellers.
In a known blower assembly, air is drawn into a housing through one or more inlet openings by the impeller. This air is then forced around the housing and out an outlet end. At least some known centrifugal blowers include a cutoff point at the transition between the arcuate blower housing and the outlet end. Blower assembly performance increases as the clearance between the backward curved impeller blade tips and the cutoff point decreases. However, when blade tips pass within close proximity to the cutoff point, they generate air pressure pulses that produce undesirable tonal noises known as blade pass pure tones, any amount of which may be objectionable to a user. Furthermore, the blade edges may generate additional pressure pulses as they pass nearby the edge of the housing inlet. These pressure pulses may also cause undesirable tonal noise.